The present invention relates generally to materials useful in forming barriers that are impervious to liquids. Such materials are often used as outer covers or baffles for disposable diapers, sanitary napkins, incontinent pads, and other products where a liquid-impervious barrier may be desired. More specifically, the present invention relates to a composite material formed from a breathable film, an apertured film, and a non-woven substrate, as well as the process for making such composite material.
Absorbent articles and products such as disposable diapers, sanitary napkins, bedpads, pantiliners, training pants, incontinent pads and garments, and the like, are items designed to be worn or placed adjacent to the body to absorb discharged bodily fluids. Bodily fluids absorbed by such products include urine, blood, menses and other excrements discharged by the body at various times.
Typically, such products are multilayered in construction and have a liquid-permeable cover, a liquid-impermeable baffle, and an absorbent material positioned in between the liquid-permeable cover and liquid-impermeable baffle. The liquid-permeable cover is designed to allow rapid transfer of bodily fluids into the absorbent layer(s) where the fluids can be retained. The baffle, which is usually an outer cover but may in some cases be positioned internally in the product, prevents leakage of the liquid retained within the absorbent area of the product. If the baffle were absent, leakage of the absorbed liquid could result in soiling of clothing, bedding, furniture, and other items positioned close to the absorbent article.
For many years, liquid-impermeable plastic films, such as polyethylene and polypropylene films, have been used to form the outer covers and baffles. Generally, such plastic films are impermeable to gases and water vapor, as well as liquids. The films prevent, or at least minimize, leakage by establishing a barrier to the passage of liquid from the absorbent article in situations where either the capacity of the absorbent article has been exceeded or the loading of the target zone has exceeded the capacity of the absorbent article to wick liquid from that target zone to liquid storage areas.
While completely liquid-impermeable films are well-suited to prevent the migration of liquid waste from the absorbent materials to the outer clothing of persons wearing such absorbent articles, the use of such liquid- and vapor-impermeable covers can result in a relatively high degree of humidity being maintained in the article when liquid has been absorbed. Oftentimes, a clammy feeling may result from this retained humidity. Such resulting clamminess also may contribute to skin irritations such as rashes if the article is left on a wearer for an extended period of time. In addition, due to the complete impermeability of such covers, the absorbent articles often feel hot to the user before being insulted with fluids.
Such completely impermeable films have been replaced in certain products with breathable, liquid-impermeable barriers. As used herein, the term xe2x80x9cbreathablexe2x80x9d means that the barrier or film is pervious to water vapor and gases. In other words, xe2x80x9cbreathable barriersxe2x80x9d and xe2x80x9cbreathable filmsxe2x80x9d allow water vapor and gases to pass therethrough, but not necessarily liquids.
In some cases, breathable, liquid-impermeable barriers are made from various nonporous breathable films which, because of their molecular structures, are impervious to liquid but not impervious to vapors. These types of breathable barriers are generally composed of sufficient amounts of polymers such as poly(vinyl alcohol) (xe2x80x9cPVOHxe2x80x9d), polyvinyl acetate (xe2x80x9cPVAxe2x80x9d), ethylene vinyl alcohol (xe2x80x9cEVAxe2x80x9d), polyurethane, ethylene methyl acrylate (xe2x80x9cEMAxe2x80x9d), and ethylene methyl acrylic acid (xe2x80x9cEMMxe2x80x9d) to make them breathable.
One such breathable, liquid-impermeable barrier is disclosed in U.S. Pat. No. 4,828,556 to Braun et al. Braun et al. is commonly owned by the assignee of the present invention and is incorporated herein in its entirety by reference. The breathable barrier of Braun et al. is a multilayered, clothlike barrier comprised of at least three layers. The first layer is a porous nonwoven web; the second layer, which is joined to one side of the first layer, comprises a continuous film of PVOH; and the third layer, which is joined to either the second layer or the other side of the first layer not joined with the second layer, comprises another porous nonwoven web. The second layer continuous film of PVOH is not microporous, i.e., nonporous, meaning that it is substantially free of voids which connect the upper and lower surfaces of the film.
In other cases, breathable films are constructed with micropores therein to provide desired levels of liquid impermeability and vapor permeability. The micropores form what is often referred to as tortuous pathways through the film. Liquid contacting one side of the film does not have a direct passage through the film. Instead, a network of microporous channels in the film prevents liquids from passing, but allows gases and water vapor to pass. Due to their structure, such films are termed for purposes of the present application as xe2x80x9cporousxe2x80x9d.
In some of such products, the breathable, liquid-impermeable barriers are made from polymer films that are highly filled with a substance such as calcium carbonate. The films are made breathable by stretching the filled films to create the microporous passageways as the polymer breaks away from the calcium carbonate during stretching.
Such porous breathable films are obviously more expensive to construct. In addition, porous breathable films are more susceptible to possible liquid penetrations than are nonporous breathable films.
An example of a breathable, yet fluid penetration-resistant material is described in U.S. Pat. No. 5,591,510 to Junker et al. The fabric material described in Junker et al. comprises a breathable outer layer of paper stock and a layer of breathable, fluid-resistant nonwoven material. The fabric also includes a thermoplastic film having a plurality of perforations which allow the film to be breathable while resisting direct flow of liquid therethrough.
Another breathable film barrier is disclosed in U.S. patent application Ser. No. 08/169,826 to McCormack. McCormack is also commonly owned by the assignee of the present invention and is incorporated herein in its entirety by reference. (The published PCT application that corresponds to this United States patent application is WO 95/16562, published on Jun. 22, 1995.) As disclosed therein, a breathable film is adhered to a fibrous polyolefin nonwoven web to form a breathable, cloth-like film/nonwoven composite. In particular, McCormack discloses a bonding agent incorporated into one or more layers of the composite which makes the layers easier to thermally bond into a composite.
Another film/nonwoven laminate is disclosed in U.S. patent application Ser. No. 08/359,987 to McCormack et al. This application is also commonly owned by the assignee of the present invention and is incorporated herein in its entirety by reference. (The PCT application corresponding to this United States patent application was published on Jun. 27, 1996, under WO 96/19346.) McCormack et al. discloses a low gauge, multilayer film, which may be laminated to other materials such as, for example, fibrous nonwoven webs. In particular, the films have a core layer made from an extrudable thermoplastic polymer and then has one or more skin layers attached to the exterior surfaces of the core layer. In some instances, the multilayer films are made breathable either through the use of specialized polymers which permit diffusion of gases through the layer and/or through the use of particulate fillers.
Other designs of breathable absorbent articles include diapers that are arranged to provide some level of breathability at the leg cuff regions of the diaper, articles that have humidity transfer regions in the form of breathable panels in otherwise vapor-impermeable outer covers, and articles having perforated regions to help the garment breath. An example of an absorbent article having a humidity transfer area is shown in U.S. Pat. No. 5,558,658 to Menard et al. This patent utilizes a liquid- and vapor-impermeable backsheet in some embodiments and a liquid-impermeable, vapor-permeable backsheet in others. Menard et al. is owned by the assignee of the present invention and is incorporated herein in its entirety by reference.
U.S. Pat. No. 4,681,793 to Linman et al. describes an absorbent article such as a diaper or sanitary napkin which utilizes a liquid-impervious backsheet. The backsheet is made from an inner layer which is provided next to an absorbent layer and an outer layer which forms the side of the article which will be farthest from the wearer""s body. The inner layer may be constructed from a substantially liquid- and vapor-impervious polymeric film such as polyethylene or from a substantially liquid-impervious, but vapor-pervious material such as a porous polytetrafluoroethylene. Linman et al. specifically notes that the uses of such porous liquid-impervious, vapor-pervious materials are more expensive than using liquid- and vapor-impervious films. The outer layer of the backsheet in this arrangement comprises a layer of polymeric film that has a number of relatively small, protuberances, each exhibiting a tiny aperture at its apex.
U.S. Pat. No. 4,341,216 to Obenour describes a two-element breathable backsheet for use on disposable diapers. The inner panel which is adjacent to the diaper""s absorbent material is made from a liquid impermeable film such as polyethylene. The outer panel is constructed so that it includes liquid- and vapor-impermeable regions as well as liquid-impermeable, vapor-pervious regions. In an alternative embodiment, Obenour states that the inner panel includes a liquid-impermeable region as well as liquid- and vapor-pervious regions. In this embodiment, the liquid- and vapor-pervious regions are preferably perforated so as to allow vapor and liquid passage.
On the other hand, the body-facing side of such absorbent articles have been designed so that they are liquid-permeable. Obviously, the side of the absorbent article facing the body should allow for quick and efficient passage of the bodily fluids into the absorbent material layer(s). For example, U.S. Pat. No. 4,690,679 to Maftingly. III et al. describes the use of an absorbent material sealed between a fluid impervious barrier and an apertured film cover. The apertured film cover described therein comprises a two-layer apertured film formed by the coextrusion of two polymers. The film is xe2x80x9caperturedxe2x80x9d in that it includes a plurality of apertures that extend from the upper surface of the film to the lower surface of the film.
Although various designs of backsheets for absorbent articles are known in the art, the presently available backsheets do not allow breathability in the manner provided by the present invention. In particular, the art is generally deficient in providing a liquid-impervious, but vapor-pervious backsheet designed to provide cloth-like aesthetics, with relatively high bulk at a relatively low cost.
It is an object of the present invention to provide an improved backsheet for forming the outer cover of an absorbent article.
It is another object of the present invention to provide an absorbent article with an improved backsheet.
Another object of the present invention is to provide a liquid-impermeable, vapor-pervious backsheet for absorbent articles.
An additional object of the present invention is to provide a liquid-impermeable, vapor-pervious backsheet for absorbent articles that exhibits certain desirable aesthetic characteristics.
Another object of the present invention is to provide a process for making a liquid-impermeable, vapor-pervious laminate that is apertured and useful as the backsheet for absorbent articles.
These and other objects are achieved by providing a breathable (vapor-pervious), liquid-impermeable apertured film/nonwoven laminate. The laminate comprises at least three layers: a nonwoven, an apertured film, and a breathable, nonporous, but liquid-impervious, film. The layers may be arranged in any sequence, meaning that the apertured film layer may be sandwiched between the breathable film layer and the nonwoven layer or the breathable film layer may be sandwiched between the apertured film layer and the nonwoven.
The nonwoven may comprise any nonwoven material and may advantageously be a spunbond, meltblown, or spunbond/meltblown spunbond material. The nonwoven may comprise single component fibers or bicomponent fibers in, for example, a sheath/core type arrangement or in a side-by-side arrangement.
The apertured film may be any thermoplastic film, including polyethylene, polypropylene, copolymers of polypropylene or polyethylene, or calcium carbonate-filled films. The particular aperturing techniques utilized to obtain the apertured film layer may be varied. The film may be formed as an apertured film or may be formed as a continuous, non-apertured film and then subjected to a mechanical aperturing process.
The particular nonporous, breathable film may be varied and includes films of poly(vinyl alcohol) (xe2x80x9cPVOHxe2x80x9d), polyvinyl acetate (xe2x80x9cPVAxe2x80x9d), ethylene vinyl alcohol (xe2x80x9cEVAxe2x80x9d), polyurethane, ethylene methyl acrylate (xe2x80x9cAMAxe2x80x9d), and ethylene methyl acrylic acid (xe2x80x9cEMAAxe2x80x9d). In addition, the breathable film may consist of mixtures of two or more breathable polymers or may be constructed from mixtures of nonbreathable polymers such as polyethylene and a sufficient amount of breathable polymer to provide the overall film with sufficient vapor-permeability characteristics to make it classifiable as breathable.
In forming the breathable film/nonwoven laminate, the desired layers may be bonded together in a number of various ways.
Thermal bonding, adhesive bonding, and sonic bonding are merely examples of various bonding techniques that may be utilized in the present process to attach either the apertured film layer or the breathable film layer to the nonwoven. The breathable film layer may be attached to the apertured film layer in various ways, including extrusion coating, thermally laminating, adhesively laminating, and sonically bonding.
The apertured film may be used in a thicknesses of from about 4 mils to about 40 mils, with such thickness being determined after the apertured film is formed. The breathable film layer will typically be used in thicknesses of from about 0.01 mils to about 5 mils. The nonwoven web layer will typically have a basis weight of from about 0.25 ounces per square yard (osy) to about 5.0 osy.
In use, the backsheet described herein may be utilized as the outer cover on a number of various absorbent articles. Such absorbent articles include disposable diapers, sanitary napkins, bedpads, pantiliners, training pants, incontinent pads and garments, and the like. The backsheet may be arranged on the absorbent article in any orientation, but preferably will be attached so that the nonwoven layer faces outward and is in contact with the clothing of the wearer and the apertured film and breathable film layers face inward towards the absorbent core of the absorbent article,
Other objects, features and aspects of the present invention are discussed in greater detail below.